(a) Field of the Invention
The invention relates to a method of preparing a cored wire suitable for use in coating metallic articles which are exposed to erodent particles. In particular, the invention relates to deposition of an erosion resistant coating which is comprised of larger ferroboron phases bound with a ductile metallic phase, said ductile metallic phase having a low affinity for oxygen.
(b) Description of the Prior Art
Solid particle erosion is defined as the progressive loss of material from a solid surface that results from repeated impact of solid particles. Solid particle erosion is to be expected whenever hard particles are entrained in a gas or liquid medium impinging on a solid at any significant velocity, generally greater than 1 m/s. Manifestations of solid particle erosion include thinning of components, a macroscopic scooping appearance following the gas-particle flow field, surface roughening which severity depends on particle size and velocity, lack of directional grooving characteristic of abrasion and, in some cases, the formation of ripple patterns.
The distinction between erosion and abrasion should be clarified, because terms are very often misunderstood and situations not adequately classed. Solid particle erosion refers to a series of particles striking and rebounding from the surface, while abrasion results from the sliding of abrasive particles across a surface under the action of an externally applied force. The clearest distinction is that, in erosion, the force exerted by the particle on the material is due to their deceleration, while in abrasion it is externally applied and constant.
Therefore, erosion is affected by three types of variables: impingement variables describing the particle flow (velocity, impingement angle and particle concentration), particle variables (particle shape, size, hardness and friability) and material microstructure. The velocity of erodent has a marked influence on the rate of material removal. It is generally admitted that the rate of erosion exponentially (the exponent being between 2 and 2.5 for metals and 2.5 and 3 for ceramics) increases with the velocity. Angular particles produce erosion rates higher than rounded ones. The hardness of erodent particles relative to the material being eroded should be considered.
Depending on their nature, materials have a different response to erosion. Material removal in ductile material involves large plastic flow while, in ceramics fracture is of primary importance, particularly for higher incidence angles. Solid particles impacting metals form plastic impact craters and displace material. At low incidence angles, the displaced material is thereafter cut and removed by a mechanism known in the scientific literature as "platelet mechanism". Metallic materials present higher erosion rate at low impact angle than at high impact angle. Conversely, ceramics are more damaged at high impact angles than at low impact angles and present erosion peak at 90.degree.. In their case, the mechanism of material removal involves cracks initiated by brittle fracture for erosion at normal incidence angle.
Thus, for particles impacting at low velocity hard materials are usually considered at low impact angle but elastic materials should be selected at high impact angle. For higher particle velocity hard materials with some toughness are selected for low impact angle and resilient materials showing a compromise between strength and ductility are chosen for high impact angles. Resilience is required to resist penetration of the surface by impacting particles. Therefore, the selection of materials to resist erosion depends on the angle at which the particles strike the surface and the impact velocity.
Two-phase materials such as high chromium white cast irons and Stellites might be expected to exhibit high erosion resistance. It could be expected that such alloys could combine the relatively good erosion of hard ceramic phase with the desirable ductility and toughness of a metal. Though these alloys provide excellent abrasion resistance, under most erosion conditions they exhibit little or no improvement over plain carbon steels or pure metals. There is a synergetic increase of the erosion of hard and brittle phase by its presence as a dispersed phase in a relatively soft metal matrix. As an example, the eroded surface of white cast iron by quartz sand shows that primary carbide are deeply depressed below the surface.
Erosion is considered as a serious problem in many engineering systems such as steam and jet turbines, pipelines and valves carrying particulate material and fluidized bed combustion systems. Generally speaking, machinery for use in processing and transportation of fluids containing solid particles are exposed to damage resulting from erosion. Processing machines for processing resins containing glass fibers, carbon fiber, asbestos or iron oxide; slurry pumps for fluid transportation of ore or coal; pipelines for transporting slurries and so forth are examples of industrial machinery that are damaged by solid particle erosion.
Particularly, high-temperature fluidized bed metal components exposed to temperatures up to 500.degree. C. and process fans that aspirate gas having temperatures that reach 350.degree. C. suffer extensive material wastage. Heat exchanger tubes in fluidized bed combustors experienced relatively high wastage rate at low temperature (250.degree. C.). The wastage rate increases with the temperature and the particle velocity. Peak wastage rates are observed for 347 stainless steel at 450.degree. C., for Incoloy 800H at 450.degree. C., for mild steel at 300.degree. C., for 1Cr-0.5Mo steel at 400.degree. C., for 2.25Cr-1Mo at 400.degree. C., for 722M24T steel at 400.degree. C. At temperatures above 100.degree. C., erosion enhances oxidation. The wastage involves the formation and removal of oxide by impacting particles. At these temperatures, thin oxide layers are formed at much greater rates than would be the case during static oxidation. Impacting particles repeatedly take off thin oxide layers, the exposed metallic surface being readily oxidized. Therefore, in these conditions, erosion accelerates the oxidation of materials.
In process fans used in pelletizing plants to re-circulate hot gas containing iron ore particles, the same type of wastage is observed. Iron ore pellets are sintered in continuous large industrial oil-fired furnaces. From the furnace, large volumes of hot gas are sucked by powerful fans. Being exposed to gas-borne iron particles and temperatures ranging between 125.degree. C. and 328.degree. C. fan components are rapidly deteriorated. Extensive part repair or replacement are required for maintaining a profitable operation.
Cobalt- and nickel-bonded tungsten carbide coatings as well as nickel-bonded chromium carbide have been widely adopted in various applications because of their wear resistance. Unfortunately, these coatings are applied using expensive high velocity oxy-fuel and plasma spraying techniques. In addition, these coating techniques are not suited for on-site applications, particularly in restricted areas. These materials contain strategic, price-sensitive elements such as nickel, chromium and tungsten and/or do not necessarily offer the best erosion resistance in applications mentioned above. These elements (WC) are either strategic or scarce, so that the carbide materials are price sensitive. In addition, elements contained within these materials present some toxicity restricting their use in some applications, requiring expensive health protection equipment and limiting personnel exposure to toxic dust.
There are many workers that have previously proposed materials based on iron and iron borides for different applications.
Kondo, Okada, Minoura and Watanabe in (U.S. Pat. No. 3,999,952) (1976) proposed a method to produce a sintered hard alloy, prepared from a hard alloy powder comprising iron boride or iron multiple boride in which a part of iron boride is substituted by a non-ferrous boride or multiple boride.
In a subsequent patent (U.S. Pat. No. 4,194,900) (1980) Ide, Takagi, Watanabe, Ohhira, Fukumori and Kondo proposed a modification in the method for producing the hard alloy powder by using different raw materials for improving strength and hardness. In these works, hard alloys are produced by crushing the hard alloy powder, pressing the milled powder and sintering the compact under vacuum or controlled atmosphere.
Ide, Kawamura, Ohhira, Watanabe and Kondo in Jap. Pat. No. Sho (1983)-101622 proposed a method of using hard sintered alloys of the iron-based complex series in combination to form paired metals. The hard phase of these alloys contains 35-96 wt. % iron-based complex boride with the remaining consisting of one or more of Cr, Fe, Mo, W, Ti, V, Nb, Ta, Hf, Zr, Ni, Co, Mn or the alloys of these metals to form the bonding phase. Sliding wear properties of the sintered alloys against metals were evaluated using the Ohgoshi sliding wear tester.
Watanabe, and Shimizu in U.S. Pat. No. 4,259,119 (1981) proposed a sintered body suitable as abrasive material comprising 70 to 99.99% of a combination of at least two kinds of metal borides selected from the group consisting of diborides of Ti, Ta, Cr, Mn, Mo, Y, Hf, Nb, Al and Zr and from 0.01 to 30% by weight of a metal boride or borides selected from the group consisting of borides of nickel, iron and cobalt.
Watanabe and Kono in U.S. Pat. No. 4,292,081 (1981) proposed sintered refractory and abrasive bodies composed of titanium diboride, chromium diboride, tantalum diboride with minor amounts of metal borides such as MnB, Mn.sub.3 B.sub.4, Mn.sub.2 B, Mn.sub.4 B, TiB, Ti.sub.2 B.sub.5, W.sub.2 B.sub.5 and Mo.sub.2 B.sub.5. In the preparation of sintered bodies iron boride, nickel borides and cobalt borides are also added to favour liquid phase sintering. Watanabe et al. in U.S. Pat. No. 5,036,028 proposed a high density metal-boride based ceramic sintered body composed of at least: a) TiB.sub.2, ZrB.sub.2, CrB.sub.2, HfB.sub.2, VB.sub.2, TaB.sub.2, NbB.sub.2, MoB.sub.2, YB.sub.2, AlB.sub.2, MgB.sub.2, CrB, VB, TaB, NbB, MoB, HfB, YB, ZrB, HfB, TiB, MnB, W.sub.2 B.sub.5 and Mo.sub.2 B.sub.5 ; b) 0.1 to 10 wt. % of cobalt boride, nickel boride or iron boride and c) 0.1 to 10 wt. % of a double carbide comprising Ti, Zr, Wand C, ZrCN, HfCN or a double carbo-nitride comprising Ti, Zr, Hf and C,N.
Jandeska and Rezhets in U.S. Pat. No. 4,678,510 (1987) proposed a wear resistant iron alloy article formed by compacting and sintering a predominantly iron powder mixture containing additions of C, Cu and nickel boride. The product microstructure comprises hard borocementite particles dispersed in a martensitic or pearlite matrix. The particles have a cross-sectioned dimension greater than 1 .mu.m, in an amount preferably between 10 and 30 volume percent to improve the wear resistance. This material was developed for automotive gears.
Saito and Kouji in Eur. pat. No. 0659894A2 proposed a high modulus iron-based alloy comprising a matrix of iron or iron alloy and one boride selected from the group consisting of borides of group Iva elements, and complex borides of group Va element and iron dispersed in the matrix. The iron based-alloy is obtained by sintering at temperature of 1000 to 1300.degree. C. The sintered product is undesirably likely to form liquid phase above 1300.degree. C. In samples 13-15, Fe-17Cr is mixed with ferrotitatium and ferroboron powders.
Miura, Arakida, Kondo and Ide in U.S. Pat. No. 4,427,446 (1984) proposed a wear-resistant composite material for use in centrifugally cast linings. The matrix metal is an oxidation-resistant nickel or cobalt alloy and the reinforcing material is a boride or a composite boride composed of chromium, iron and boron. The matrix used is either a Ni--Cr--B--Si based self-fluxing alloy or a Co--Ni--Cr--W--B--Si based self-fusing alloy. According to the inventors, the self-fluxing properties of alloys which melt at temperature comprised between 950 and 1250.degree. C. is the key point of their process. The cylinder containing a powder mixture comprising the self-fluxing alloy and the reinforcement is first heated to the melting temperature of the alloy. Placed in a centrifuge, the melt is allowed to cool slowly. After cooling, the inner surface is rich in reinforcing particles.
Clark and Sievers in U.S. Pat. No. 4,389,439 (1983) proposed a different lining for tubes and cylinders. They proposed a composite tubing comprising an iron boride layer formed in situ by the diffusion of boron into iron. The diffusion coating obtained has an inner layer comprising dispersed iron carbide and an outer layer consisting of iron boride.
Sanchez-Caldera, Lee, Suh and Chun in U.S. Pat. No. 5,071,618 (1991) proposed a method for manufacturing a dispersion-strengthened material based on a metal matrix with a containing element capable of reacting with boron and a second metal containing metal and boron. The material is produced by injecting the two metal in liquid state at two different speeds. It produces materials containing boride particles having an average size of 0.2 .mu.m.
Dallaire and Champagne in U.S. Pat. No. 4,673,550 (1987) proposed a process for synthesizing TiB.sub.2 composite materials containing a metallic phase. The preparation of these composites comprises providing mixture titanium alloys which in addition contain Fe, Ni, Al, Mo, Cr, Co, Cu or mixtures thereof and boron or ferroboron. After heating, it results in the synthesis of composite material containing fine TiB.sub.2 crystals dispersed in a metallic matrix. Coatings applied by plasma spraying possess excellent abrasion wear resistance.
Jackson and Myers in U.S. Pat. No. 3,790,353 (1974) proposed a hard facing pad usable, for example, by brazing to a digger tooth or the like. The wear pad is from 70 to 85 per cent per volume particles of cemented carbide in a metal matrix having a melting point not substantially higher than the melting point of the metal cementing the carbide.
Tagaki, Mori, Kawasaki and Kato in U.S. Pat. No. 5,004,581 (1991) proposed a dispersion strengthened copper-base alloy for wear resistant overlay formed on a metal substrate consisting in 5-30 wt. % Ni, 0.5-3 wt. % B, 1-5 wt. % Si, 4-30 wt. % Fe, 3-15 wt. % Sn or 3-30 wt. % An, the remaining being copper. It forms boride and silicide of the Ni--Fe system dispersed in a copper-base matrix. This material is expected to provide a superior wear-resistance to slide abrasion as evaluated by the Ohgoshi abrasion tester.
Gale, Helton and Mueller in U.S. Pat. No. 3,970,445 (1976) proposed a wear-resistant alloy comprising boron, chromium an iron having high hardness produced by rapidly cooling and solidifying spheroidal particles of the molten alloy mixture. The resultant particles are cast in the desired form or incorporated into a composite alloy wherein the solid particles are held together with a matrix of different material from the alloy. This alloy was designed for use in abrasive environments (ground-engaging tools). The composite particles comprise 25-61 wt. % chromium, 6-12 wt. % boron and the balance iron and are produced by melting.
Helton, Gale, Moen, Mueller, Pierce and Vermillion in U.S. Pat. No. 4,011,051 (1977) proposed spheroidal particles of wear-resistant alloy comprising boron, chromium and iron with high hardness produced by the rapid cooling of a molten alloy mixture. The resultant solid particles are then incorporated into a composite alloy wherein the solid particles are held together with a matrix of different material from the alloy. Inserts of the alloy are useful in producing long wearing tools. The composite particles contain 25-70 wt. % chromium, 6-12 wt. % boron, 0-2 wt. % carbon, the remaining being iron. One of the brazing alloy consist in 94.0 wt. % nickel, 3.5 wt. % silicon, 1.5 wt. % boron, 1.25 wt. % iron and 0.03 wt. % carbon.
Helton, Gale, Moen, Mueller, Pierce and Vermillion in U.S. Pat. No. 4,113,920 (1978) proposed a ground engaging tool resisting to wear including a contact section for engaging the ground and at least a portion of said section reinforced with a wear resistant alloy, said wear resistant alloy comprising cast spherical of a first alloy embedded in a matrix of a second alloy in which said first alloy is soluble with difficulty and wherein the first alloy comprises from about 25-70 wt. % chromium, from about 6-12 wt. % boron, from about 0 to about 2 wt. % carbon, and iron is the balance. The matrix is a nickel based brazing alloy. Mixed powders are jointed by conventional sintering processes.
Moen in U.S. Pat. No. 4,066,422 (1978) proposed a wear-resistant composite material and method of making an article which is particularly adaptable for use with a ground engaging tool. The composite material comprises abrasive-wear resistant particles embedded in a matrix consisting of about 3 to 5 wt. % boron, and the balance being iron having residual impurities. The boron is controlled to a level of approximately 3.8 wt. % corresponding to the eutectic Fe--B composition which has the low melting temperature of 1161.degree. C.
E. I. Larsen in U.S. Pat. No. 3,720,990 (1973) disclosed a molybdenum alloy containing at least two metallic elements which form an alloy which melts at a temperature considerably below that of molybdenum and when in the molten state dissolves appreciable molybdenum during liquid phase sintering and which may be shaped before or after sintering, thus avoiding expensive hot working and/or hot forging.
Babu in U.S. Pat. No. 4,235,630 (1980) and Can. Pat. No. 1,110,881 (1981) proposed a wear-resistant molybdenum-iron boride alloy having a microstructure of a primary boride phase and a matrix phase. The primary boride phase comprises molybdenum alloyed with iron and boron, and the matrix phase comprises one of boron-iron in iron and iron- molybdenum in iron. The alloy finds particular utility in a composite material on a ground-engaging tool. The alloy is densified by sintering the article at a temperature sufficient for controlled formation of a liquid phase. The molybdenum-iron-boride alloy can be also crushed to form particles that can be bounded by a suitable matrix, such as the iron-boron matrix composition described in U.S. Pat. No. 4,066,422 attributed to Moen. For fabricating the sintered alloy Babu used in examples a preferred ferroboron constituent containing 25 wt. % boron.
Dudko, Samsonov, Maximovich, Zelenin, Klimanov, Potseluiko, Trunov and Sleptsov in Can. Pat. No. 1,003,246 (1977) proposed wear-resistant composite materials for hard facing equipment subjected to abrading. Particulate material containing 7-30 wt. % chromium, 40-60 wt. % titanium and 30-40 wt. % boron having a size between 0.3 to 2 mm are embedded in a low-melting alloy matrix to ensure good wettability. Preferred alloys contain: a) 30-65 wt. % copper, 10-35 wt. % nickel and 10-35 wt. % manganese; b) 12-25 wt. % chromium, 1.5-4 wt. % silicon, 1-4 wt. % boron, the balance being nickel.
Ray in U.S. Pat. No. 4,133,679 (1979) described glassy alloys containing iron and molybdenum or tungsten, together with low boron content. The glassy alloys consist essentially of about 5 to 12 atom percent boron, a member selected from the group consisting of about 25 to 40 atom percent molybdenum and about 13 to 25 atom percent tungsten and the balance iron plus incidental impurities.
The prior art references described above relate to compositions of matter which differ from those of the subject application. Alternatively, the physical properties of the subject invention, namely hard ferroboron phases of relatively large area bound with a ductile metallic phase, provide an erosion resistant coating which is surprisingly superior to prior art coatings.